ACPAtmospheric Chemistry and PhysicsACPAtmos. Chem. Phys.1680-7324Copernicus GmbHGöttingen, Germany10.5194/acp-10-2867-2010The organic fraction of bubble-generated, accumulation mode Sea Spray Aerosol (SSA)ModiniR. L.1HarrisB.1RistovskiZ. D.11ILAQH, Queensland University of Technology, P.O. Box 4233, Brisbane QLD, 4001, Australia2603201010628672877This work is licensed under a Creative Commons Attribution 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/This article is available from http://www.atmos-chem-phys.net/10/2867/2010/acp-10-2867-2010.htmlThe full text article is available as a PDF file from http://www.atmos-chem-phys.net/10/2867/2010/acp-10-2867-2010.pdf

Recent studies have detected a dominant accumulation mode
(~100 nm) in the Sea Spray Aerosol (SSA) number
distribution. There is evidence to suggest that particles in this mode
are composed primarily of organics. To investigate this hypothesis we
conducted experiments on NaCl, artificial SSA and natural SSA
particles with
a Volatility-Hygroscopicity-Tandem-Differential-Mobility-Analyser
(VH-TDMA). NaCl particles were atomiser generated and a bubble
generator was constructed to produce artificial and natural SSA
particles. Natural seawater samples for use in the bubble generator
were collected from biologically active, terrestrially-affected
coastal water in Moreton Bay, Australia. Differences in the
VH-TDMA-measured volatility curves of artificial and natural SSA
particles were used to investigate and quantify the organic fraction
of natural SSA particles. Hygroscopic Growth Factor (HGF) data, also
obtained by the VH-TDMA, were used to confirm the conclusions drawn
from the volatility data. Both datasets indicated that the organic
fraction of our natural SSA particles evaporated in the VH-TDMA over
the temperature range 170–200 &deg;C. The organic volume fraction
for 71–77 nm natural SSA particles was 8&plusmn;6%. Organic
volume fraction did not vary significantly with varying water
residence time (40 s to 24 h) in the bubble generator
or SSA particle diameter in the range 38–173 nm. At room
temperature we measured shape- and Kelvin-corrected HGF at 90% RH of
2.46&plusmn;0.02 for NaCl, 2.35&plusmn;0.02 for artifical SSA and
2.26&plusmn;0.02 for natural SSA particles. Overall, these results
suggest that the natural accumulation mode SSA particles produced in
these experiments contained only a minor organic fraction, which had
little effect on hygroscopic growth. Our measurement of 8&plusmn;6% is
an order of magnitude below two previous measurements of the organic
fraction in SSA particles of comparable sizes. We stress that our results were
obtained using coastal seawater and they can't necessarily be applied on a
regional or global ocean scale. Nevertheless, considering the order of
magnitude discrepancy between this and previous studies, further research
with independent measurement techniques and a variety of different
seawaters is required to better quantify how much organic material is present
in accumulation mode SSA.